Recombinant alphavirus particles (alphavirus replicon particles) have great potential for use in protein production, antigen delivery, and various therapeutic applications. Alphavirus packaging cell lines (PCL) are the most efficient and cost effective way to generate alphavirus replicon particles. One obstacle in the development of alphavirus packaging cell lines, however, is the low particle yield. On the other hand, generation of RCV (replication competent viral particles) is a potential problem when generating large numbers of recombinant alphavirus particles. The probability of recombination can be greatly reduced by dividing the defective helpers in two separate cassettes, because multiple switches would be required to produce an infectious RNA. However, it is possible that large-scale production could still generate RCV. Thus, there is a need in the art for methods of increasing the productivity of PCL and of reducing the possibility that replication competent virus may be generated during large scale production of recombinant alphavirus particles.